A single Value

## A single Value A single Value — Assorted functions for dealing with GValue values. |

## Synopsis

    GValue *            gda_value_new                       (GType type);
    #define             gda_value_new_null                  ()
    GValue *            gda_value_copy                      (const GValue *value);
    void                gda_value_free                      (GValue *value);
    GValue *            gda_value_new_from_string           (const gchar *as_string,
                                                             GType type);
    gboolean            gda_value_set_from_string           (GValue *value,
                                                             const gchar *as_string,
                                                             GType type);
    gboolean            gda_value_set_from_value            (GValue *value,
                                                             const GValue *from);
    void                gda_value_set_null                  (GValue *value);
    gchar *             gda_value_stringify                 (const GValue *value);
    gint                gda_value_differ                    (const GValue *value1,
                                                             const GValue *value2);
    gint                gda_value_compare                   (const GValue *value1,
                                                             const GValue *value2);
    GValue *            gda_value_new_from_xml              (const xmlNodePtr node);
    xmlNodePtr          gda_value_to_xml                    (const GValue *value);
    void                gda_value_reset_with_type           (GValue *value,
                                                             GType type);
    gboolean            gda_value_is_null                   (const GValue *value);
    gboolean            gda_value_is_number                 (const GValue *value);
    #define             gda_value_isa                       (value, type)

                        GdaBinary;
    GValue *            gda_value_new_binary                (const guchar *val,
                                                             glong size);
    const GdaBinary *   gda_value_get_binary                (const GValue *value);
    void                gda_value_set_binary                (GValue *value,
                                                             const GdaBinary *binary);
    void                gda_value_take_binary               (GValue *value,
                                                             GdaBinary *binary);
    gpointer            gda_binary_copy                     (gpointer boxed);
    void                gda_binary_free                     (gpointer boxed);
    gchar *             gda_binary_to_string                (const GdaBinary *bin,
                                                             guint maxlen);
    GdaBinary *         gda_string_to_binary                (const gchar *str);

                        GdaBlob;
    GValue *            gda_value_new_blob                  (const guchar *val,
                                                             glong size);
    GValue *            gda_value_new_blob_from_file        (const gchar *filename);
    gpointer            gda_blob_copy                       (gpointer boxed);
    void                gda_blob_free                       (gpointer boxed);
    const GdaBlob *     gda_value_get_blob                  (const GValue *value);
    void                gda_value_set_blob                  (GValue *value,
                                                             const GdaBlob *blob);
    void                gda_value_take_blob                 (GValue *value,
                                                             GdaBlob *blob);
    void                gda_blob_set_op                     (GdaBlob *blob,
                                                             GdaBlobOp *op);
    gchar *             gda_blob_to_string                  (GdaBlob *blob,
                                                             guint maxlen);

                        GdaGeometricPoint;
    gpointer            gda_geometricpoint_copy             (gpointer boxed);
    void                gda_geometricpoint_free             (gpointer boxed);
    const GdaGeometricPoint * gda_value_get_geometric_point (const GValue *value);
    void                gda_value_set_geometric_point       (GValue *value,
                                                             const GdaGeometricPoint *val);

    typedef             GdaValueList;
    const GdaValueList * gda_value_get_list                 (const GValue *value);
    void                gda_value_set_list                  (GValue *value,
                                                             const GdaValueList *val);

                        GdaNumeric;
    gpointer            gda_numeric_copy                    (gpointer boxed);
    void                gda_numeric_free                    (gpointer boxed);
    const GdaNumeric *  gda_value_get_numeric               (const GValue *value);
    void                gda_value_set_numeric               (GValue *value,
                                                             const GdaNumeric *val);

                        GdaTime;
    gpointer            gda_time_copy                       (gpointer boxed);
    void                gda_time_free                       (gpointer boxed);
    const GdaTime *     gda_value_get_time                  (const GValue *value);
    void                gda_value_set_time                  (GValue *value,
                                                             const GdaTime *val);

                        GdaTimestamp;
    gpointer            gda_timestamp_copy                  (gpointer boxed);
    void                gda_timestamp_free                  (gpointer boxed);
    const GdaTimestamp * gda_value_get_timestamp            (const GValue *value);
    void                gda_value_set_timestamp             (GValue *value,
                                                             const GdaTimestamp *val);
    GValue *            gda_value_new_timestamp_from_timet  (time_t val);

    gshort              gda_value_get_short                 (const GValue *value);
    void                gda_value_set_short                 (GValue *value,
                                                             const gshort val);

    gushort             gda_value_get_ushort                (const GValue *value);
    void                gda_value_set_ushort                (GValue *value,
                                                             const gushort val);

## Description

Libgda manages each individual value within an opaque GValue structure. Any GValue type can be used, and Libgda adds a few more data types usually found in DBMS such as NUMERIC, TIME, TIMESTAMP, GEOMETRIC POINT, BINARY and BLOB.

Libgda makes a distinction between binary and blob types

- binary data can be inserted into an SQL statement using a (DBMS dependant) syntax, such as "X'ABCD'" syntax for SQLite or the binary strings syntax for PostgreSQL. Binary data is manipulated using a GdaBinary structure (which is basically a bytes buffer and a length attribute).

- blob data are a special feature that some DBMS have which requires some non SQL code to manipulate them. Usually only a reference is stored in each table containing a blob, and the actual blob data resides somewhere on the disk (while still being managed transparently by the database). For example PotsgreSQL stores blobs as files on the disk and references them using object identifiers (Oid). Blob data is manipulated using a GdaBlob structure which encapsulates a GdaBinary structure and adds a reference to a GdaBlobOp object used to read and write data from and to the blob.

Please note that is distinction between binary data and blobs is Libgda only and does not reflect the DBMS's documentations; for instance MySQL has several BLOB types but Libgda interprets them as binary types.

Each provider or connection can be queried about its blob support using the `gda_server_provider_supports_feature()` or `gda_connection_supports_feature()` methods.

The NULL value is a special case value: it is represented by to a zero-filled (uninitialized) GValue and has a type equal to GDA_TYPE_NULL.

## Details

### gda_value_new ()

    GValue *            gda_value_new                       (GType type);

Makes a new GValue of type `type`.

`type` : | the new value type.
Returns : | the newly created GValue with the specified `type`. You need to set the value in the returned GValue.

### gda_value_new_null()

    #define                           gda_value_new_null() (g_new0 (GValue, 1))

Returns : |

### gda_value_copy ()

    GValue *            gda_value_copy                      (const GValue *value);

Creates a new GValue from an existing one.

`value` : | value to get a copy from.
Returns : | a newly allocated GValue with a copy of the data in `value`.

### gda_value_free ()

    void                gda_value_free                      (GValue *value);

Deallocates all memory associated to a GValue.

`value` : | the resource to free.

### gda_value_new_from_string ()

    GValue *            gda_value_new_from_string           (const gchar *as_string,
                                                             GType type);

Makes a new GValue of type `type` from its string representation.

For more information about the string format, see the `gda_value_set_from_string()` function. This function is typically used when reading configuration files or other non-user input that should be locale independent.

`as_string` : | stringified representation of the value.
`type` : | the new value type.
Returns : | the newly created GValue or `NULL` if the string representation cannot be converted to the specified `type`.

### gda_value_set_from_string ()

    gboolean            gda_value_set_from_string           (GValue *value,
                                                             const gchar *as_string,
                                                             GType type);

Stores the value data from its string representation as `type`.

The accepted formats are:

- G_TYPE_BOOLEAN: a caseless comparison is made with "true" or "false"

- numerical types: C locale format (dot as a fraction separator)

- G_TYPE_DATE: see `gda_parse_iso8601_date()`

- GDA_TYPE_TIME: see `gda_parse_iso8601_time()`

- GDA_TYPE_TIMESTAMP: see `gda_parse_iso8601_timestamp()`

This function is typically used when reading configuration files or other non-user input that should be locale independent.

`value` : | a GValue that will store `val`.
`as_string` : | the stringified representation of the value.
`type` : | the type of the value
Returns : | `TRUE` if the value has been converted to `type` from its string representation; it not means that the value is converted successfully, just that the transformation is avairable. `FALSE` otherwise.

### gda_value_set_from_value ()

    gboolean            gda_value_set_from_value            (GValue *value,
                                                             const GValue *from);

Sets the value of a GValue from another GValue. This is different from gda_value_copy, which creates a new GValue. gda_value_set_from_value, on the other hand, copies the contents of `copy` into `value`, which must already be allocated.

`value` : | a GValue.
`from` : | the value to copy from.
Returns : | `TRUE` if successful, `FALSE` otherwise.

### gda_value_set_null ()

    void                gda_value_set_null                  (GValue *value);

Sets the type of `value` to GDA_TYPE_NULL.

`value` : | a GValue that will store a value of type GDA_TYPE_NULL.

### gda_value_stringify ()

    gchar *             gda_value_stringify                 (const GValue *value);

Converts a GValue to its string representation which is a human readable value. Note that the returned string does not take into account the current locale of the user (on the contrary to the GdaDataHandler objects). Using this function should be limited to debugging and values serialization purposes.

Dates are converted in a YYYY-MM-DD format.

`value` : | a GValue.
Returns : | a new string, or `NULL` if the conversion cannot be done. Free the value with a `g_free()` when you've finished using it.

### gda_value_differ ()

    gint                gda_value_differ                    (const GValue *value1,
                                                             const GValue *value2);

Tells if two values are equal or not, by comparing memory representations. Unlike `gda_value_compare()`, the returned value is boolean, and gives no idea about ordering.

The two values must be of the same type, with the exception that a value of any type can be compared to a GDA_TYPE_NULL value, specifically:

- if `value1` and `value2` are both GDA_TYPE_NULL values then the returned value is 0

- if `value1` is a GDA_TYPE_NULL value and `value2` is of another type then the returned value is 1

- if `value1` is of another type and `value2` is a GDA_TYPE_NULL value then the returned value is 1

- in all other cases, `value1` and `value2` must be of the same type and their values are compared

`value1` : | a GValue to compare.
`value2` : | the other GValue to be compared to `value1`.
Returns : | a non 0 value if `value1` and `value2` differ, and 0 if they are equal

### gda_value_compare ()

    gint                gda_value_compare                   (const GValue *value1,
                                                             const GValue *value2);

Compares two values of the same type, with the exception that a value of any type can be compared to a GDA_TYPE_NULL value, specifically:

- if `value1` and `value2` are both GDA_TYPE_NULL values then the returned value is 0

- if `value1` is a GDA_TYPE_NULL value and `value2` is of another type then the returned value is -1

- if `value1` is of another type and `value2` is a GDA_TYPE_NULL value then the returned value is 1

- in all other cases, `value1` and `value2` must be of the same type and their values are compared

`value1` : | a GValue to compare (not `NULL`)
`value2` : | the other GValue to be compared to `value1` (not `NULL`)
Returns : | if both values have the same type, returns 0 if both contain the same value, an integer less than 0 if `value1` is less than `value2` or an integer greater than 0 if `value1` is greater than `value2`.

### gda_value_new_from_xml ()

    GValue *            gda_value_new_from_xml              (const xmlNodePtr node);

Creates a GValue from an XML representation of it. That XML node corresponds to the following string representation: <value type="gdatype">value</value>

For more information about the string format, see the `gda_value_set_from_string()` function. This function is typically used when reading configuration files or other non-user input that should be locale independent.

`node` : | an XML node representing the value.
Returns : | the newly created GValue.

### gda_value_to_xml ()

    xmlNodePtr          gda_value_to_xml                    (const GValue *value);

Serializes the given GValue to an XML node string.

`value` : | a GValue.
Returns : | the XML node. Once not needed anymore, you should free it.

### gda_value_reset_with_type ()

    void                gda_value_reset_with_type           (GValue *value,
                                                             GType type);

`value` : |
`type` : |

### gda_value_is_null ()

    gboolean            gda_value_is_null                   (const GValue *value);

Tests if a given `value` is of type GDA_TYPE_NULL.

`value` : | value to test.
Returns : | a boolean that says whether or not `value` is of type GDA_TYPE_NULL.

### gda_value_is_number ()

    gboolean            gda_value_is_number                 (const GValue *value);

Gets whether the value stored in the given GValue is of numeric type or not.

`value` : | a GValue.
Returns : | `TRUE` if a number, `FALSE` otherwise.

### gda_value_isa()

    #define gda_value_isa(value, type) (G_VALUE_HOLDS(value, type))

`value` : |
`type` : |

### GdaBinary

    typedef struct {
    	guchar *data;
    	glong   binary_length;
    } GdaBinary;

### gda_value_new_binary ()

    GValue *            gda_value_new_binary                (const guchar *val,
                                                             glong size);

Makes a new GValue of type GDA_TYPE_BINARY with value `val`.

`val` : | value to set for the new GValue.
`size` : | the size of the memory pool pointer to by `val`.
Returns : | the newly created GValue.

### gda_value_get_binary ()

    const GdaBinary *   gda_value_get_binary                (const GValue *value);

`value` : | a GValue whose value we want to get.
Returns : | the value stored in `value`.

### gda_value_set_binary ()

    void                gda_value_set_binary                (GValue *value,
                                                             const GdaBinary *binary);

Stores `val` into `value`.

`value` : | a GValue that will store `val`.
`binary` : | a GdaBinary structure with the data and its size to be stored in `value`.

### gda_value_take_binary ()

    void                gda_value_take_binary               (GValue *value,
                                                             GdaBinary *binary);

Stores `val` into `value`, but on the contrary to `gda_value_set_binary()`, the `binary` argument is not copied, but used as-is and it should be considered owned by `value`.

`value` : | a GValue that will store `val`.
`binary` : | a GdaBinary structure with the data and its size to be stored in `value`.

### gda_binary_copy ()

    gpointer            gda_binary_copy                     (gpointer boxed);

Creates a new GdaBinary structure from an existing one.

`boxed` : | source to get a copy from.
Returns : | a newly allocated GdaBinary which contains a copy of information in `boxed`.

### gda_binary_free ()

    void                gda_binary_free                     (gpointer boxed);

Deallocates all memory associated to the given GdaBinary.

`boxed` : | GdaBinary to free.

### gda_binary_to_string ()

    gchar *             gda_binary_to_string                (const GdaBinary *bin,
                                                             guint maxlen);

Converts all the non printable characters of bin->data into the "\xyz" representation where "xyz" is the octal representation of the byte, and the '\' (backslash) character is converted to "\\".

Note that the backslash and newline characters are considered as printable characters and will not be represented by the "\xyz" representation.

Use this function to get a representation as much readable by humans as possible of a binary chunk. Note that this function is internally called when transforming a binary value to a string for example when using `g_value_transform()` or `gda_value_stringify()`.

`bin` : | a correctly filled `GdaBinary` structure
`maxlen` : | a maximum len used to truncate, or 0 for no maximum length
Returns : | a new string from `bin`

### gda_string_to_binary ()

    GdaBinary *         gda_string_to_binary                (const gchar *str);

Performs the reverse of `gda_binary_to_string()` (note that for any "\xyz" succession of 4 characters where "xyz" represents a valid octal value, the resulting read value will be modulo 256)

`str` : | a string to convert
Returns : | a new GdaBinary if no error were found in `str`, or NULL otherwise

### GdaBlob

    typedef struct {
    	GdaBinary  data;
    	GdaBlobOp *op;
    } GdaBlob;

Represents some binary data, accessed through a GdaBlobOp object. `op` is generally set up by database providers when giving access to an existing BLOB in a database, but can be modified if needed using `gda_blob_set_op()`.

GdaBinary `data`; | data buffer, as a GdaBinary
GdaBlobOp *`op`; | a pointer to a GdaBlopOp, or `NULL`

### gda_value_new_blob ()

    GValue *            gda_value_new_blob                  (const guchar *val,
                                                             glong size);

Makes a new GValue of type GDA_TYPE_BLOB with the data contained by `val`.

`val` : | value to set for the new GValue.
`size` : | the size of the memory pool pointer to by `val`.
Returns : | the newly created GValue.

### gda_value_new_blob_from_file ()

    GValue *            gda_value_new_blob_from_file        (const gchar *filename);

`filename` : |
Returns : |

### gda_blob_copy ()

    gpointer            gda_blob_copy                       (gpointer boxed);

Creates a new GdaBlob structure from an existing one.

`boxed` : | source to get a copy from.
Returns : | a newly allocated GdaBlob which contains a copy of information in `boxed`.

### gda_blob_free ()

    void                gda_blob_free                       (gpointer boxed);

Deallocates all memory associated to the given GdaBlob.

`boxed` : | GdaBlob to free.

### gda_value_get_blob ()

    const GdaBlob *     gda_value_get_blob                  (const GValue *value);

`value` : | a GValue whose value we want to get.
Returns : | the value stored in `value`.

### gda_value_set_blob ()

    void                gda_value_set_blob                  (GValue *value,
                                                             const GdaBlob *blob);

Stores `val` into `value`.

`value` : | a GValue that will store `val`.
`blob` : | a GdaBlob structure with the data and its size to be stored in `value`.

### gda_value_take_blob ()

    void                gda_value_take_blob                 (GValue *value,
                                                             GdaBlob *blob);

Stores `val` into `value`, but on the contrary to `gda_value_set_blob()`, the `blob` argument is not copied, but used as-is and it should be considered owned by `value`.

`value` : | a GValue that will store `val`.
`blob` : | a GdaBlob structure with the data and its size to be stored in `value`.

### gda_blob_set_op ()

    void                gda_blob_set_op                     (GdaBlob *blob,
                                                             GdaBlobOp *op);

correctly assigns `op` to `blob`

`blob` : | a GdaBlob value
`op` : | a GdaBlobOp object, or `NULL`

### gda_blob_to_string ()

    gchar *             gda_blob_to_string                  (GdaBlob *blob,
                                                             guint maxlen);

Converts all the non printable characters of blob->data into the \xxx representation where xxx is the octal representation of the byte, and the '\' (backslash) character is converted to "\\".

`blob` : | a correctly filled `GdaBlob` structure
`maxlen` : | a maximum len used to truncate, or 0 for no maximum length
Returns : | a new string from `blob`

### GdaGeometricPoint

    typedef struct {
    	gdouble x;
    	gdouble y;
    } GdaGeometricPoint;

### gda_geometricpoint_copy ()

    gpointer            gda_geometricpoint_copy             (gpointer boxed);

`boxed` : |
Returns : |

### gda_geometricpoint_free ()

    void                gda_geometricpoint_free             (gpointer boxed);

`boxed` : |

### gda_value_get_geometric_point ()

    const GdaGeometricPoint * gda_value_get_geometric_point (const GValue *value);

`value` : | a GValue whose value we want to get.
Returns : | the value stored in `value`.

### gda_value_set_geometric_point ()

    void                gda_value_set_geometric_point       (GValue *value,
                                                             const GdaGeometricPoint *val);

Stores `val` into `value`.

`value` : | a GValue that will store `val`.
`val` : | value to be stored in `value`.

### GdaValueList

    typedef GList GdaValueList;

### gda_value_get_list ()

    const GdaValueList * gda_value_get_list                 (const GValue *value);

`value` : | a GValue whose value we want to get.
Returns : | the value stored in `value`.

### gda_value_set_list ()

    void                gda_value_set_list                  (GValue *value,
                                                             const GdaValueList *val);

Stores `val` into `value`.

`value` : | a GValue that will store `val`.
`val` : | value to be stored in `value`.

### GdaNumeric

    typedef struct {
    	gchar   *number;
    	glong    precision;
    	glong    width;
    	gpointer reserved; /* reserved for future usage with GMP (http://gmplib.org/) */
    } GdaNumeric;

### gda_numeric_copy ()

    gpointer            gda_numeric_copy                    (gpointer boxed);

Creates a new GdaNumeric structure from an existing one.

`boxed` : | source to get a copy from.
Returns : | a newly allocated GdaNumeric which contains a copy of information in `boxed`.

### gda_numeric_free ()

    void                gda_numeric_free                    (gpointer boxed);

Deallocates all memory associated to the given `boxed`

`boxed` : | a GdaNumeric pointer

### gda_value_get_numeric ()

    const GdaNumeric *  gda_value_get_numeric               (const GValue *value);

`value` : | a GValue whose value we want to get.
Returns : | the value stored in `value`.

### gda_value_set_numeric ()

    void                gda_value_set_numeric               (GValue *value,
                                                             const GdaNumeric *val);

Stores `val` into `value`.

`value` : | a GValue that will store `val`.
`val` : | value to be stored in `value`.

### GdaTime

    typedef struct {
    	gushort hour;
    	gushort minute;
    	gushort second;
    	gulong  fraction;
    	glong   timezone;	/* # of seconds to the east UTC */
    } GdaTime;

### gda_time_copy ()

    gpointer            gda_time_copy                       (gpointer boxed);

`boxed` : |
Returns : |

### gda_time_free ()

    void                gda_time_free                       (gpointer boxed);

`boxed` : |

### gda_value_get_time ()

    const GdaTime *     gda_value_get_time                  (const GValue *value);

`value` : | a GValue whose value we want to get.
Returns : | the value stored in `value`.

### gda_value_set_time ()

    void                gda_value_set_time                  (GValue *value,
                                                             const GdaTime *val);

Stores `val` into `value`.

`value` : | a GValue that will store `val`.
`val` : | value to be stored in `value`.

### GdaTimestamp

    typedef struct {
    	gshort  year;
    	gushort month;
    	gushort day;
    	gushort hour;
    	gushort minute;
    	gushort second;
    	gulong  fraction;
    	glong   timezone;	/* # of seconds to the east UTC */
    } GdaTimestamp;

gshort `year`; | representation of the date
gushort `month`; | month representation of the date, as a number between 1 and 12
gushort `day`; | day representation of the date, as a number between 1 and 31
gushort `hour`; |
gushort `minute`; |
gushort `second`; |
gulong `fraction`; |
glong `timezone`; |

### gda_timestamp_copy ()

    gpointer            gda_timestamp_copy                  (gpointer boxed);

`boxed` : |
Returns : |

### gda_timestamp_free ()

    void                gda_timestamp_free                  (gpointer boxed);

`boxed` : |

### gda_value_get_timestamp ()

    const GdaTimestamp * gda_value_get_timestamp            (const GValue *value);

`value` : | a GValue whose value we want to get.
Returns : | the value stored in `value`.

### gda_value_set_timestamp ()

    void                gda_value_set_timestamp             (GValue *value,
                                                             const GdaTimestamp *val);

Stores `val` into `value`.

`value` : | a GValue that will store `val`.
`val` : | value to be stored in `value`.

### gda_value_new_timestamp_from_timet ()

    GValue *            gda_value_new_timestamp_from_timet  (time_t val);

Makes a new GValue of type GDA_TYPE_TIMESTAMP with value `val` (of type time_t).

`val` : | value to set for the new GValue.
Returns : | the newly created GValue.

### gda_value_get_short ()

    gshort              gda_value_get_short                 (const GValue *value);

`value` : | a GValue whose value we want to get.
Returns : | the value stored in `value`.

### gda_value_set_short ()

    void                gda_value_set_short                 (GValue *value,
                                                             const gshort val);

Stores `val` into `value`.

`value` : | a GValue that will store `val`.
`val` : | value to be stored in `value`.

### gda_value_get_ushort ()

    gushort             gda_value_get_ushort                (const GValue *value);

`value` : | a GValue whose value we want to get.
Returns : | the value stored in `value`.

### gda_value_set_ushort ()

    void                gda_value_set_ushort                (GValue *value,
                                                             const gushort val);

Stores `val` into `value`.

`value` : | a GValue that will store `val`.
`val` : | value to be stored in `value`.

## See Also

The GdaBlobOp object which operates on blobs